// 在json里添加‘全部’标签
     let newA={
       id:0,
       name:'全部',
       depth:2,
       pid:0,
       children: null
     }
     for(let i=1;i<this.shengShi.length-3;i++){
       this.shengShi[i].children.shift()
       this.shengShi[i].children.unshift(newA)
     }
    console.log(this.shengShi)



// 级联框
<el-cascader
                  v-model="shiValue"
                  :options="shengShi"
                  :props="optionProps"
                  placeholder="请选择地区"
                  @change="cityChange"
                >
                </el-cascader>
data() {
    return {
      // 重新命名
      optionProps:{
        value:'id',
        label:'name',
        // children:'',
        // checkStrictly: true 
      },
  }
},
methods: {
  cityChange(value) {
      // console.log(value);
      console.log(this.shiValue)
    },
}


// city.json
[{
    "id": 1,
    "name": "北京",
    "depth": 1,
    "pid": 0,
    "children": [
      {
        "id": 0,
        "name": "全部",
        "depth": 2,
        "pid": 0,
        "children": null
      }]
}]


